Flexible circuits

ABSTRACT

The present invention provides a circuit creation technology that improves conductive line manufacture by adding active and elemental palladium onto the surface of a substrate. The palladium is disposed in minute amounts on the surface and does not form a conductive layer by itself, but facilitates subsequent deposition of a metal onto the surface, according to the pattern of the palladium, to form the conductive lines.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to co-pendingU.S. patent application Ser. No. 11/854,274, entitled “FLEXIBLECIRCUITS,” filed Sep. 12, 2007, by Sharma et al., which in turn claimspriority under 35 U.S.C. §119(e) to U.S. Provisional Application No.60/999,733, entitled “FLEXIBLE CIRCUITS”, filed Sep. 12, 2006, by Sharmaet al, both of which are incorporated herein by reference in theirentireties for all purposes.

TECHNICAL FIELD

This invention relates to precursors used to facilitate the depositionof a metal onto a surface, such as metal used to form conductive linesin a circuit. In particular, the invention relates to printing circuitprecursors on a wide variety of substrates including flexible andnon-flat substrates.

BACKGROUND

Circuit manufacturers employ numerous techniques to deposit a conductivepattern on a substrate. One technique applies a conductive seed layer tothe substrate to facilitate subsequent electro/electroless plating of ametal that forms conductive lines in the conductive pattern. Theconductive seed layer alone is insufficient to reliably serve as theconductive lines in a circuit, but uses large amounts of the seedmaterial to maintain conductivity for subsequent metal addition. Anothertechnique uses an adhesive layer to attach a conductive layer to thesubstrate. The adhesive layer, however, adds thickness to the finalcircuit, which is undesirable for circuits employed in portable andsmall form factor applications. Circuit manufacturers have alsodeveloped etching processes that apply a photoresist, etch thephotoresist to form a pattern, add metal to form conductive linesaccording to the pattern, along with other process steps such as washesto cleanse byproducts from each stage. These numerous etch stepsincrease manufacturing complexity, add disposal requirements for etchby-products, lengthen manufacturing time, and the pattern and etchequipment raises capital cost for circuit manufacture. All thesedownsides burden circuit manufacturers by adding to manufacturingcomplexity and circuit cost.

Also, most conductive pattern manufacturing processes limit theircircuits to rigid substrates. For example, a seed conductive layer needsan inflexible substrate to physically support the continuous seed layer.If the substrate bends, then the continuous and conductive seed linescrack and break, which compromises subsequent metal deposition.

The ability to manufacture a conductive pattern without these unduecomplexities and limitations would be desirable.

SUMMARY

The present invention improves conductive pattern formation and addsactive and elemental palladium onto the surface of a substrate. Activepalladium is palladium metal that has two desirable properties: it iscatalytic for subsequent addition of a metal onto the palladium, and itis strongly anchored to the underlying substrate. The active palladiumis disposed in minute amounts on the surface and does not form aconductive layer by itself, but facilitates subsequent deposition of ametal onto the surface, according to the pattern of the palladium, toform a conductive pattern. The conductive pattern may include one ormore conductive lines, or a block deposition of metal according to othershapes that do not resemble lines.

This conductive pattern formation is well suited for use in circuitmanufacture, and find wide use to create both existing and new products.For example, the present invention enables and eases printing ofconductive lines onto flexible substrates and substrates with customshapes.

In one embodiment, the active palladium is disposed on the surface byfirst depositing palladium precursor solution onto the substrate;evaporating solvent from the solution, and then decomposing a palladiumprecursor (left after the evaporation) to produce active palladium onthe substrate surface. The active palladium may or may not be patternedto regulate subsequent deposition of a metal according to the pattern.Active palladium patterning may be accomplished during solutiondeposition on the surface or during decomposition, for example.

In one aspect, the present invention relates to a method for producingactive palladium on a substrate. The method includes depositing apalladium precursor solution onto the substrate; the palladium precursorsolution includes a Lewis base ligand and a palladium compound in asolvent. The method also includes exposing the palladium precursorsolution to conditions that promote evaporation of the solvent from thepalladium precursor solution to leave a palladium precursor on thesubstrate. The method further includes decomposing the palladiumprecursor to produce a pattern of active palladium on a surface of thesubstrate, wherein the active palladium approximately has a zerovalence.

In another aspect, the present invention relates to another method forproducing active palladium on a substrate. The method includes providinga solution comprising a) a Lewis base ligand and b) a palladiumcarboxylate having three to five carbon atoms in c) a solvent. Asuitable organic solvent may include an aprotic and polar solvent. Themethod also includes depositing a portion of the palladium precursorsolution onto the substrate. The method further includes removing thesolvent to leave a palladium precursor on the substrate. The methodadditionally includes decomposing the palladium precursor to leaveactive palladium on the substrate.

In yet another aspect, the present invention relates to a circuitprecursor that includes a substrate and a pattern of active palladium ona surface of the substrate. The active palladium does not form aconductive layer on the substrate and has a surface concentration ofless than about 6×10⁻¹⁰ gram atoms of palladium per square millimeter.

In still another aspect, the present invention relates to a method forproviding a palladium precursor solution for use with a printer. Themethod comprises adding a Lewis base ligand and a palladium carboxylateto a solvent to create a palladium precursor solution. The method alsocomprises storing the palladium precursor solution in a printingreservoir for use with the printer, which is configured to transfer thepalladium precursor solution from the reservoir onto a substrate.

In another aspect, the present invention relates to a circuit thatincludes a substrate, a pattern of active palladium on a surface of thesubstrate, and a set of conductive lines that include a metal and aredisposed on the substrate according to the active palladium pattern. Theactive palladium does not form a conductive layer on the substrate andhas a surface concentration of less than about 6×10⁻¹⁰ gram atoms ofpalladium per square millimeter.

In yet another aspect, the present invention relates to a method forproducing one or more conductive lines on a substrate. The methodincludes depositing a palladium precursor solution onto the substrate,wherein the palladium precursor solution includes a Lewis base ligandand a palladium compound in a solvent. The method also includes exposingthe palladium precursor solution to conditions that promote evaporationof the solvent to leave a palladium precursor on the substrate. Themethod further includes decomposing the palladium precursor to leaveactive palladium on the substrate, wherein the active palladiumapproximately has a zero valance. The method additionally includesdepositing a metal on the substrate according to a pattern of the activepalladium on the substrate to form one or more conductive lines.

In still another aspect, the present invention relates to a structureincluding a substrate, a conductive layer disposed on the substrate, anda layer of active palladium disposed between the substrate and theconductive layer. The active palladium does not form a conductive layeron the substrate without depositing a metal or conductive material layerand has a surface concentration of less than about 6×10⁻¹⁰ gram atoms ofpalladium per square millimeter.

In another aspect, the present invention relates to a method forprinting a palladium precursor on a flexible substrate. The methodincludes printing a palladium precursor solution onto the substrateusing a printer. The palladium precursor solution includes a Lewis baseligand and a palladium compound in a solvent. The method also includesexposing the palladium precursor solution to conditions that promoteevaporation of the solvent from the palladium precursor solution toleave a palladium precursor on the substrate.

In yet another aspect, the present invention relates to a printingapparatus for printing a circuit or a circuit precursor. The printingapparatus comprises a reservoir configured to contain a palladiumprecursor solution. The solution includes a solvent, a Lewis base ligandin the solvent, and a palladium carboxylate in the solvent, wherein thepalladium carboxylate has six carbon atoms or less. The printingapparatus also comprises a dispensing mechanism configured to transferthe palladium precursor solution from the reservoir to a substrate.

In still another aspect, the present invention relates to a liquid foruse with a printer to produce a metal precursor pattern on a substrate.The liquid includes a palladium precursor solution suitable for printingin the printer onto the substrate. The solution includes a solvent, aLewis base ligand in the solvent, and a palladium carboxylate in thesolvent.

In another aspect, the present invention relates to a liquid for usewith a printing apparatus to produce a metal precursor pattern on asubstrate. The liquid includes a palladium precursor solution suitablefor printing in the printing apparatus onto the substrate. The solutionincludes a solvent, a Lewis base ligand in the solvent, and a palladiumcarboxylate in the solvent. The palladium precursor solution is adaptedto a rheological property of a fluidic dispensing requirement of theprinting apparatus.

In yet another aspect, the liquid includes an additive that adjusts arheological property of the palladium precursor solution to arheological property of a fluidic dispensing requirement of the printingapparatus

These and other features and advantages of the invention will bedescribed in more detail below with reference to the associated figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method for producing active palladium on a substrate inaccordance with one embodiment of the present invention.

FIG. 2 shows a method for manufacturing a printed circuit on a substratein accordance with one embodiment of the present invention.

FIG. 3 shows simplified cross sections of exemplary manufacturedcomponents obtained using the manufacturing of FIG. 2 in accordance withone embodiment of the present invention.

FIG. 4A illustrates an exemplary active palladium pattern on a surfaceof a circuit in accordance with a specific embodiment of the presentinvention.

FIG. 4B shows an illustrative microscopic view of a single palladiumline from FIG. 4A.

FIG. 4C illustrates initial radial growth of copper from the palladiumatoms on a surface of a substrate, according to growth that might bewitnessed in an electroless plating process for example.

FIG. 4D illustrates a circuit produced according to the exemplary activepalladium pattern of FIG. 4A.

FIG. 5 shows the production of a printing reservoir that storespalladium ink in accordance with one embodiment of the presentinvention.

FIG. 6A shows the printing reservoir used with a printing apparatus inaccordance with one embodiment of the present invention.

FIG. 6B shows a printing reservoir that includes palladium precursorsolution in accordance with a specific embodiment of the presentinvention.

FIG. 7 shows an expanded cross section of a structure in accordance witha specific embodiment of the present invention.

FIG. 8 illustrates a continuous throughput manufacturing process inaccordance with one embodiment of the present invention.

FIG. 9A illustrates an exemplary RFID device in accordance with aspecific embodiment of the present invention.

FIG. 9B illustrates the automated manufacturing process of the RFIDdevice of FIG. 9A according to techniques of the present invention.

FIG. 9C shows exemplary printed output of the manufacturing process ofFIG. 9B, which includes numerous RFID devices on a roll material, inaccordance with a specific embodiment of the present invention.

FIG. 10A shows a tracking label that includes a layered design inaccordance with a specific embodiment of the present invention.

FIG. 10B shows an inner surface of a housing used in a cell phone thatincludes a conformal surface and circuit printed thereon in accordancewith a specific embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

Circuit manufacturing methods described herein deposit a metal precursorto a substrate, before adding one or more conductive lines. The metalprecursor refers to a metal, typically in elemental form, that catalyzesthe deposition of another metal onto a surface. Copper is a common metalthat is added to form conductive lines. Numerous established metalplating processes, such as electro/electroless plating, are used incircuit manufacturing to deposit copper onto a surface to form theconductive lines, and benefit from a metal precursor as describedherein. High-resolution circuits and circuit boards may be printed inthis manner—on flexible substrates and custom shaped surfaces. Metallicand non-metallic substrates may also be used in the circuits, includingthermoplastic substrates, thermosetting resins, glass, ceramics,semiconductor materials including silicon, etc.

Active palladium is a metal precursor that works well with manysubstrates and copper deposition techniques. The active palladium hastwo desirable properties: (1) it is catalytic for subsequent addition ofa metal onto the palladium (such as electroless deposition), and (2) itis strongly anchored to the underlying substrate. In one embodiment, theactive palladium approximately has a zero valance. The active palladiumis also ideally disposed monoatomically onto the substrate. One of skillin the art will appreciate that elemental palladium does not readilybind to a surface monoatomically or with an approximately zero valance,and needs to be deliberately processed to achieve such a state.Described below are processing techniques to accomplish this.

FIG. 1 shows a method 50 for producing a metal precursor such as activepalladium on a substrate in accordance with one embodiment of thepresent invention. Although the present invention will now be describedas a method, those of skill in the art will recognize that descriptionprovided for the following steps and method may also apply to one ormore apparatus used to implement the methods and/or a device produced bythe steps and method.

FIG. 2 shows a method 70 for manufacturing a printed circuit on asubstrate in accordance with one embodiment of the present invention,which includes the metal precursor patterning steps 52-56 of FIG., 1 inaddition to several steps related to circuit design and manufacture.FIG. 3 shows simplified cross sections of exemplary manufacturedcomponents obtained using the manufacturing of FIG. 2 in accordance withone embodiment of the present invention.

Beginning with FIG. 1, metal precursor patterning method 50 begins bydepositing a palladium precursor solution onto a substrate 20. In oneembodiment, the palladium precursor solution includes a Lewis baseligand and a palladium compound in a solvent. Further description ofpalladium precursor solutions and chemical constituents included thereinare described in further detail below.

The palladium precursor solution is exposed to conditions that promoteevaporation of the solvent from the palladium precursor solution, toleave a palladium precursor on the substrate (54). Typically thisincludes supplying heat to the substrate and/or solution via conduction,convection and/or radiation. For example, a field evaporation usingconvection is suitable for many printing applications. While the goal ofthis evaporation step is generally to remove as much as the solvent aspossible, it is understood that incomplete solvent evaporation issuitable for many embodiments. In this case, additional heat or energysupplied in the next step may complete the evaporation process.

In one embodiment, evaporation at least partially occurs before thedroplets of palladium precursor solution settle on the substrate. Insome cases, the method expedites evaporation by pre-heating thepalladium precursor solution while it is being deposited on to thesubstrate. Depending on the substrate, evaporating the solvent before orduring decomposition reduces local inaccuracies that may result from theactive palladium (which is so reactive that it may bind to the solvent)attaching to the solvent residue.

Method 50 then decomposes the palladium precursor to produce a patternof active and elemental palladium on a surface of the substrate (56).The decomposition adds energy to the palladium precursor to separate andremove the ligand from the elemental palladium, thereby leaving theelemental palladium on the surface. As will be described in furtherdetail below, the decomposition facilitates the deposition of monoatomicand elemental palladium with approximately zero valence on thesubstrate. In one embodiment, the decomposition converts the palladiumprecursor from a palladium cation to active palladium atoms withapproximately zero valence on the substrate.

Decomposition and de-ligation may be accomplished in various manners.Generally speaking, the decomposition apparatus provides electromagneticradiation and energy to the substrate and/or palladium precursor.Suitable energy sources may include thermal sources, light sources suchas a laser, infrared and ultraviolet heaters, ion beams, e-beams,microwave sources, and combinations thereof. The radiation source may becoherent or non-coherent. In one embodiment, electromagnetic radiationtuned to a particular wavelength is employed to minimize thermal energytransfer and emphasize chemical reaction. For example, ultravioletradiation may be employed to promote many different chemicaldecomposition reactions. Further, microwave energy may be employed forpalladium inks where the anion or ligand has hydroxyl groups, as thehydroxyl absorbs radiation in the microwave range. Decomposing apalladium precursor may be performed in the same chamber as theevaporation process, or a different one.

Spatial control for the decomposition is useful when a pattern has notalready been established, e.g., during deposition of the solution ontothe substrate. In a specific embodiment, a guided laser, ion beam ore-beam, is employed to provide a pattern on the surface by locallydecomposing the palladium precursor according to the beam movement.

Decomposition proceeds sensitive to the substrate. For example, meltingtemperature of the substrate—relative to the decomposition temperatureof the palladium precursor—will affect temperatures used duringdecomposition. If the substrate melting temperature is higher than thedecomposition temperature for the palladium precursor, thendecomposition may use heat at a temperature between the two withoutcompromising the substrate. In another embodiment where the substratemelting temperature is less than or near the decomposition temperatureof the palladium precursor, the decomposition provides heat (or anotherform of energy) to the palladium precursor at short bursts or pulses toovercome the decomposition threshold of the palladium precursor, whileavoiding damage to the substrate. This is also useful for anyrelationship between the substrate melting (or softening) temperatureand the decomposition temperature for the palladium precursor (e.g.,when the substrate melting temperature is greater than the decompositiontemperature of the palladium precursor) to save energy for thedecomposition.

In one embodiment, a pattern of active palladium is formed when thepalladium precursor solution is deposited on the substrate. This permitsevaporation and decomposition to be spatially imprecise. Subsequentevaporation and decomposition of the palladium precursor then occursspatially on the substrate according to the established pattern ofsolution and palladium precursor. For example, various liquid printingtechnologies such as conventional inkjet printers may be used to patternthe palladium precursor solution at desired locations on a flat ornon-flat substrate. Resolution of the active palladium pattern thenrelates to the spatial resolution of the printing technology used todispense the solution.

In a specific embodiment, decomposition (56) only occurs afterevaporation (54) in order to avoid smudging of a deposited palladiumprecursor solution pattern and compromise of a spatially precisepattern. Further discussion of palladium precursor solution printing isdescribed with respect to FIG. 6A.

In another embodiment, the palladium precursor solution is depositedwithout a pattern, and localized decomposition forms a pattern of activepalladium from a blanket layer of palladium precursor. For example, aguided laser, ion beam or e-beam may be used to scribe specificlocations on a blanket sheet of palladium precursor on a surface,according to a desired pattern. 2-D or 3-D beam control then permits theactive palladium pattern to be produced on custom shaped 2-D or 3-Dsurfaces, with a pattern resolution determined by beam actuation andguidance.

Output of method 50 of FIG. 1 is a circuit precursor that includesactive palladium on a surface of the substrate (patterned or notpatterned). FIG. 2 expands active palladium production of method 50 forthe production of a circuit.

Method 70 begins by selecting a suitable substrate (72). The choice ofsubstrate is typically driven by a particular application for thepalladium ink pattern. At a high level, the substrate may be conductive,semi conductive, or insulating. Thus, the dielectric constant of thematerial may be of any value. The substrate may be homogeneous orheterogeneous in terms of the material it is made from. As an example ofa heterogeneous substrate, packaging for a semiconductor chip includes adielectric substrate on which conductive vias are formed. Line tracesdefined by a palladium ink pattern may be patterned to connect oneconductive via to another or a conductive via to an external lead orpin.

The substrate can be flat or topologically varying. An example of anon-flat substrate is the inner casing of a cell phone that has a convexand custom shape. As another example, pins on a connector may be printedwith palladium ink. The connector may also include a custom or non-flatshape.

Also, the substrate may be rigid, flexible or semi rigid. There aremultiple ways to characterize a flexible substrate, including elasticmodulus and/or thickness. In one embodiment, a flexible substrateincludes an elastic modulus less than about 1 GPa. In a more specificembodiment, a flexible substrate includes an elastic modulus less thanabout 100 MPa. In one embodiment, a flexible substrate includes athickness less than about 1 centimeter. In a more specific embodiment,the thickness is less about 1 millimeter. A higher modulus of elasticityand/or thickness may also be used.

One substrate of particular interest is polyimid. Polyimid (also sold asKapton®) is commercially available in thin sheets, is suitable forprinting using many printers such as commercially available ink jetprinters, and is also suitable for circuit applications that include aflexible substrate. Polyimid also includes a robust thermal stabilitythat can withstand dual-stage heating as described in FIG. 1.Conventionally, adhesives are used to attach palladium to polyimid. Theadhesives remain in the finished circuit but do not survive elevatedcircuit temperatures and thus compromise the thermal stability ofpolyimid circuits (in addition to adding thickness as described above).The present invention, however, maintains thermal stability of circuitsconstructed with high temperature substrates such as polyimid, in athinner profile.

Other exemplary substrates may include polyester, polypropylene,polyethylene, ceramic materials, or any other good dielectric material.The substrate onto which the palladium precursor is deposited, andsubsequently a palladium layer and conductive lines formed, can also bea metallic material. Also, the substrate can be plastic, ceramic, glass,silicon wafer, cellulose, graphite, and paper substrates. Paper readilypermits printing using commercially available and general-purposeprinters. In general, substrate selection is driven by an application.Many rigid circuit board applications use silicon wafers and Fr4substrates.

The present invention may also use fibrous materials as a substrate,such as those used in a weave. For example, Kevlar strands may be dippedin a palladium precursor solution and further processed according toFIG. 1 to leave active palladium on the individual strands. The strainsmay then be woven according to conventional weaving techniques before orafter copper or conductive lines are disposed on the strands (e.g. byelectroless and electroplating).

Returning back to FIG. 2, the substrate may be pre-treated or cleaned,before the palladium precursor solution is added, to facilitatesubsequent processing. Various cleaning processes are suitable for use,as one of skill in the art will appreciate. For example, a bath inisopropanol simply and inexpensively cleans many polymer surfaces.Cleaning is not necessary. One advantage of the invention is that thesubstrate requires relatively little or sometimes no treatment prior todeposition of the palladium precursor solution and forming of copperlines.

The palladium precursor solution is then provided for printing (74).More detail on solution chemistry is provided below, in addition toexamples of reservoirs for storing and shipping the palladium precursorsolution (FIGS. 5, 6A and 6B).

Palladium deposition then proceeds according to FIG. 1 (steps 52-56).Output of method 50 is a pattern of palladium on a surface of thesubstrate, where the pattern substantially resembles a desiredconductive line or circuit pattern.

A pattern of active palladium refers to one or more surface areas on asubstrate that the active palladium occupies after decomposition. Aswill be described further below, the pattern may be established at anumber of stages, e.g., during deposition using a printer or duringdecomposition using a spatially controlled decomposition beam. In oneembodiment, the pattern includes a set of active palladium linesdisposed on one or more surfaces of the substrate. Often, the patternresembles a set of conductive lines to be subsequently produced usingthe pattern of active palladium. FIG. 4A illustrates an exemplary activepalladium pattern 105 on a surface 21 of a circuit 100 in accordancewith a specific embodiment of the present invention. Exemplary patternsalso include circles, rectangles, sets of concentric circles orrectangles used for an antenna, etc. In general, the present inventionis not limited to any specific pattern, and contemplates that thepattern may take any geometric arrangement.

In another embodiment, the pattern is a field deposition that covers alarge portion of the substrate surface. Thus, an active palladium andconductive layer may also be field deposited on a substrate usingmethods described herein. FIG. 7 shows an expanded cross section of asubstrate structure with a field deposition, without patterning of theactive palladium 22, in accordance with a specific embodiment of thepresent invention.

The field deposition can be considered a blanket pattern, and has manyuses. For example, a field coating is well suited for electromagneticshielding or antenna manufacture. A field coating is also well suitedfor irregular shaped objects. In this case, the irregular shapedobject—such as a strip of hook and loop fasteners, a brush, or asponge—is dipped in a palladium precursor solution to apply a fielddeposition to the many and minute features (and the solution decomposedusing an oven for example). An antenna can be made from oddly shapedobjects in this manner. Thus, the present invention is also not limitedby the shape of the substrate.

Returning to FIG. 4A, circuit 100 is disposed on a flexible tape ofpolyimid. Pattern 105 includes a series of palladium lines 102 that areshaped to facilitate the subsequent formation of conductive lines 112(FIG. 4D). Production of lines 102 and pattern 105 will be described infurther detail below.

FIG. 4B shows an illustrative microscopic view of a single palladiumline 102. The palladium line 102 includes a series of separate anddisconnected active palladium atoms 104 on the surface 21 of substrate20. Since the metal ions 104 are not connected, palladium line 102 isnot conductive.

Collectively, the palladium atoms 104 on surface 21 approximately have azero valence. It is understood that some atoms may have a slightlydifferent valence due to processing disturbances and imperfections.

Borderlines 107 are dotted to illustrate that they approximateboundaries for the deposition of active palladium ions 104. As will bedescribed with respect to FIG. 4C, copper initially accumulates onsurface 21 according to the atomic locations of palladium 104. In someinstances, depending on the how much metal is added the metal depositionprocess, copper accumulation may extend outside of borderlines 107.

Palladium deposition according to the present invention uses low surfaceconcentrations of active palladium. At a minimum, deposition generatesenough palladium on the surface to form metal conductive lines accordingto a subsequent metal deposition technique. For example, for electrolesscopper deposition, the palladium surface concentration is high enough toinitiate electroless plating. In one embodiment, palladium line 102 hasa surface concentration of less than about 6×10⁻¹⁰ gram atoms ofpalladium per square millimeter. In this case, the active and elementalpalladium 104 surface concentration is so low that the palladium 104does not form a conductive layer on substrate 20. In other words, whilesome atoms may contact, palladium 104 generally does not leave a highenough surface density to have consistent contact to permit conductivityof electrons along palladium lines 102. In a specific embodiment,palladium line 102 has a surface concentration of less than about 3×10⁻⁷gram atoms of palladium per square millimeter. It is understood thatsome of these concentrations may not be visible to a human eye withoutmagnification.

Referring to FIGS. 2 and 4C-4D, conductive line formation (76) uses oneor more metal deposition techniques that benefit from the presence ofactive palladium atoms on a surface of the substrate. Metals suitablefor use for the conductive lines may include copper, gold, nickel silverand cobalt alloys. For example, the conductive line may includepalladium atoms disposed under a copper layer with a thin outer layer ofgold deposited over the copper. Other metals may be used for conductiveline formation.

As one of skill in the art will appreciate, a wide variety of conductiveline formation techniques are suitable for use with the presentinvention. Plating is the general name of surface-covering techniques inwhich a metal is coated onto a solid surface. Numerous plating methodsconventionally used today may benefit from active palladium. Suchtechniques include: vapor deposition under vacuum, sputtering, chemicalvapour deposition with or without a vacuum, and other methods usingvacuum or gas conditions. Thin film deposition plating techniques haveaccomplished plating on scales as small as the width of an atom.Metallizing refers to the process of coating metal on non-metallicobjects. One metallizing technique suitable for use herein applies a twostep process that: a) deposits copper on a seed layer palladium patternby electroless deposition (using a conventional copper electrolessdeposition process); and b) uses electroplating to add more copper ontop of the electroless copper to produce thicker copper lines. Otherconductive line formation techniques are also suitable for use herein,and in general, the present invention is not limited to any particularmanufacturing technique for creating conductive lines on a surface thatalready includes a palladium precursor.

FIG. 4C illustrates initial radial growth of copper from palladium atoms104 on surface 21 of substrate 20. This illustration approximates coppergrowth that might be witnessed in an electroless plating process, forexample. As shown, the active palladium 104 anchor to the substrate 20and initiate attachment of copper on surface 21 according to theirlocation. The newly attached copper then facilitates further radialcopper deposition (and platelet-like growth). Copper thus accumulatesradially from each palladium ion 104 on surface 21 of substrate 20, asindicated by temporal growth lines 106.

As electroless copper deposition proceeds, contact between adjacentcopper growth lines 106 occurs. Continued metal deposition adds enoughmetal to form and gain electrical conductivity along lines 112.

The copper deposition also occurs normal to surface 21 (normal to thepage as shown). Notably, then, as copper deposition continues, theinitial palladium atoms are buried under the aggregating copper and nolonger visible. For the circuit shown in FIG. 4D, it is most likely thatno active palladium ions 104 will be visible since they are all buriedunder considerably much more copper. And given that the amount of activepalladium ions 104 is relatively small compared to the amount of copper,detection of palladium 104 becomes difficult after conductive lines 112have been formed.

In this manner, the active and elemental palladium 104 disposed onsurface 21 acts as a seed to catalyze deposition of a metal on substrate20. Controlled spatial patterning of palladium lines 102 then permitsuncontrolled patterning of conductive lines 112, which blindly followsthe established spatial pattern and arrangement of palladium lines 102.

While FIG. 4A shows one specific active palladium pattern 105, thepresent invention is not restricted to any specific number orarrangement of lines. Typically, the active palladium patternsubstantially resembles the conductive line pattern included in circuitafter copper deposition is finished. In some cases, palladium lines 102may be slightly thinner than conductive lines 112 to permit forexpansion of the conductive lines during copper deposition in one ormore stages, e.g., electroless deposition followed by electroplating. Aswill be described in further detail below, the present invention alsopermits active palladium patterns on 3-D and custom shaped surfaces.

It should be noted that the palladium printed substrate 100 of FIG. 4Acan be an end product by itself. In other words, a manufacturer may beresponsible for printing partially manufactured circuits 100 that do notyet include conductive lines. These partially manufactured circuits 100are then provided to a second manufacturer responsible for adding ametal to form the actual conductive lines.

The palladium precursor solution may be delivered to a substrate in anyof a number of different manners. In one embodiment, the solution isdelivered only to selective regions of the substrate according to adesired pattern. This spatial selectivity is referred to herein as“printing” the palladium precursor solution on the substrate. In otherembodiments, the palladium precursor solution coats the entire substrateor a large portion thereof. This may be accomplished via a printer(where the entire surface is selected for printing), dip coating, oranother blank printing procedure. In such cases, the blank palladiumprecursor solution may or may not be subsequently patterned to producethe pattern. When dispersed by a printer or automated printing process,the palladium precursor solution may be considered, and referred toherein, as an ‘ink’ or a ‘palladium ink’.

FIG. 5 shows the production of a printing reservoir that stores apalladium ink in accordance with one embodiment of the presentinvention. FIG. 6B shows a printing reservoir 200 (the output of FIG. 5)that includes palladium precursor solution 210 in accordance with aspecific embodiment of the present invention. FIG. 6A shows the printingreservoir 200 used with a printing apparatus 180 in accordance with oneembodiment of the present invention. While printing according to FIGS.6A and 6B will now be described with respect to an apparatus, those ofskill the art will recognize of the following description also appliesto methods and steps for producing printed circuit precursors.

Referring initially to FIG. 6A, printing apparatus 180 refers to amechanized system that delivers palladium precursor solution 210 onto asubstrate to form a circuit precursor 23. Printing apparatus 180generally includes: controller 182, dispensing mechanism 184, andpalladium ink reservoir 200.

The exact structure of printing apparatus 180 and each of its componentswill vary with the printing technique employed, as one of skill in theart will appreciate. Indeed, an advantage of the present invention isthat it may use a commercially available printing technique or apparatuswithout the need for special retooling or reconfiguration for printingpalladium precursor solution 210. In other cases, printing apparatus 180is specially manufactured and/or configured for printing circuitsaccording to techniques described herein.

The printing apparatus 180 may include a contact or contact-lessprinting technology, and/or signal-directed, manual or mechanical means.For example, printing apparatus 180 may employ any one, or acombination, of the following printing technologies: ink-jet printing,screen printing, pad-printing, spray coating, spin coating, puddlecoating, dip coating, Gravure printing, ultrasonic spray techniques,wire coating, a stencil, rotogravure, flexographic techniques, brushcoating, or various other blank coating techniques. Monochrome printingis suitable in many instances. A specific printing technology may beselected according to its benefits for a particular application. Forexample, ultrasonic spray techniques are well suited to deposit uniformthickness coatings.

Dispensing mechanism 184 is configured to transfer the palladiumprecursor solution 210 from reservoir 200 to a substrate 20. Thestructure of dispensing mechanism 184 will depend on the printingtechnology used. For example, a conventional inkjet printer oftenincludes a small printing tube with a known volumetric capacity that thepalladium ink fills into. A control signal causes an actuator, such as apiezoelectric actuator, to squeeze the tube and dispense ink from thetube onto the substrate. For 2-D inkjet printing, a linear actuatormoves the tube in a direction orthogonal to a direction of substratefeed, thereby providing 2-D printing onto a substrate. The tube thenexpands and contracts according to an applied waveform or control signalthat matches a known position of the tube relative to a current positionof the substrate. In this manner, any custom pattern 105 (FIG. 4A) maybe disposed on a substrate according to a control signal thatcorresponds to the pattern.

In a specific embodiment, printing apparatus 180 includes ageneral-purpose printer. For example, this may include a printertraditionally used with personal computers and commercially availablefrom a wide variety of vendors, including retail vendors and the like.One suitable personal printer is the Epson C66, available from a widevariety of vendors, reconfigured with an ink cartridge that includespalladium ink as described herein. The general-purpose printer may alsoinclude any printer used in the printing industry, such as commerciallyavailable models used to print on banners and large sheets. One suitablelarger printer is the Roland SP300V available from Roland DG Corporationof Hamamatsu, Japan. These general-purpose printers are generallyconfigured to print on thin sheets made from substrates such ascommercially available paper or polyimid. One suitable commerciallyavailable printer includes ink-jet printers. The present invention thenstores palladium precursor solution 210 in a printing cartridge 200 thatmechanically interfaces with the general-purpose printer.

Printing apparatus 180 may also be configured to interact with apersonal computer, which is used to supply printing patterns to printer180. A user interface on the personal computer permits external controlof printing on apparatus 180. The user interface also permits easyreconfiguration and printing of new patterns and circuit designs—withoutspecial retooling of printing apparatus 180 for each new pattern orcircuit. In this manner, new circuits may be printed as readily as aconventional general-purpose printer produces new paper documents.

One suitable class of printing may be broadly characterized as “drop ondemand” printing. In these processes, a drop of palladium ink is createdwherever necessary on a substrate as regulated by controller 182.Controller 182 may include any combination of a processor and/or memorysuitable configured to output a signal to control dispensing mechanism184. In one embodiment, the signal is digital and corresponds to apattern for the palladium precursor. The pattern may be received from anexternal computer that controller 182 interfaces with. Controller 182may include one or more commercially available processors that interactwith a memory that stores instructions and information suitable forprinting patterns on one more substrates. The memory may include RAM,ROM, hard drive space, tempering memory such as a memory stick orCD-ROM, etc.

Spatially controlled printers permit easy and fast circuitreconfiguration where only the control signal needs to be changed toproduce a new circuit design or layout. Thus, the present inventioncontemplates circuit manufacture according to digital design withoutmechanical reconfiguration or downtime of a circuit manufacturing line.For example, some commercially available inkjet printers are suitablefor printing circuit precursors 23 on flexible polyimid substrates oneor two at a time (or more, if desired). This permits researchorganizations, universities and other small businesses to own customcircuit manufacturing technology, without having to outsource theproduction of one or two custom circuits. Thus, the present inventioncontemplates business models where printers are sold with the intent ofenabling small organizations to do their own circuit printing andmanufacture.

Another class of printing may be broadly characterized as “image”printing. For example, Gravure printing may also be used for printingapparatus 180. As a dispensing mechanism 184, Gravure printing employs adepressed or sunken surface for the image that is etched or engravedinto a cylinder; the unetched areas of the cylinder represent thenon-image or unprinted areas. The cylinder rotates in a bath of inkcalled the ink pan (in this instance, reservoir 200 includes a Gravureink pan that stores palladium precursor solution 210). As the cylinderturns, the excess ink is wiped off the cylinder by a doctor blade. Thepalladium ink remaining on the cylinder forms a palladium pattern 105 bydirect transfer to the substrate (paper, polyimid or other material) asit passes between a plate cylinder and an impression cylinder. Gravureprinting is well suited for static image, long run, high qualityprinting that produces a sharp, fine image.

In another embodiment, printing apparatus 180 permits conformalprinting. Conformal printing refers to printing palladium ink 210 onnon-flat and three-dimensional surfaces. For example, the non-flatsurface may include the inner surface of a cell phone housing or otherportable electronics device, which is commonly curved and custom shaped.In one embodiment, conformal printing apparatus 180 includes a pen,movable in three dimensions, that dispenses palladium ink 210 inresponse to a control signal. Based on a known position of thecontrolled pen relative to the non-flat substrate, ink is released atcontrolled times and a pattern is then produced on the conformal surfaceas desired.

The conformal printing apparatus 180 may include any robotic system thattracks: a) the substrate (or part such as a cell phone housing); b) thedispensing mechanism 184; or c) combinations thereof, to provide 3-Drelative motion between the substrate and dispensing mechanism 184. Forexample, dispensing mechanism 184 may include a 3-D robotic actuatorthat moves a pen or dispensing mechanism to the custom shape of anon-flat substrate.

Resolution of a printed palladium pattern 105 (and subsequent conductiveline resolution) will vary with the printing apparatus 180. In general,resolution may be limited to droplet size for the printing apparatus. Insome cases, printing capabilities of the printing technology may be usedto improve resolution and pattern output. For example, the dots or dropsper inch used in an inkjet printer will affect droplet size and may betailored to increase pattern resolution. In addition, for manyconventional and general-purpose inkjet printers, a grayscale levelsetting changes the number of passes that the dispensing mechanism makesacross a substrate. Decreasing the grayscale setting then decreases thenumber of passes that the dispensing mechanism makes, and therebyreduces the number of drops and quantity of palladium deposited onto thesubstrate. In one embodiment, printing apparatus 180 provides a printingresolution for a printed palladium pattern 105 of about 10 microns. Inanother specific embodiment, a line density of greater than about 1 lineper millimeter is suitable for use. A printing resolution of about 100microns is suitable in many applications. In another embodiment,printing apparatus 180 outputs droplets between about 15 and about 20picoliters.

Line thickness is another suitable measure of printing resolution. Inone embodiment, the present invention prints lines with a planarthickness up to about 2 microns. In a specific embodiment, a palladiumpattern includes a line with a surface width of less than about 250microns. Thicker lines may be used. As one of skill in the art willappreciate, the line width and spacing will depend on the printingtechnology and desired pattern.

It is understood that some printers may use multiple passes to achievethe desired palladium concentration on a surface. For example, aprinting apparatus may print a palladium precursor solution, having aconcentration of palladium of about 0.01, five times to achieve adesired concentration on the substrate (such as 0.05). This permitslower concentrations of palladium and solution to be used in a printingreservoir.

Various processes and printing apparatus for blanket depositing ofpalladium ink may also be employed. A blanket deposition involvescoating a large portion or the entire substrate surface with thepalladium ink and without defining a pattern. Dip coating represents onesuitable method for blanket deposition of palladium ink Dip coatingallows substrates in any shape and size to have palladium precursorsolution disposed thereon. For example, strands and fibers such as thoselater weaved together may be dip coated, in addition to non-flatsurfaces described above.

The blanketed palladium precursor is then later altered to produce adesired pattern. Patterning a palladium pattern 105 onto a blank ink ofdeposition is referred to in here as ‘scribing’. In one embodiment,scribing occurs during decomposition of the palladium precursorremaining after the solvent is evaporated off. As mentioned above,decomposition typically includes adding energy to the palladiumprecursor. One suitable scribing process uses a laser writing process.While the palladium precursor is adhered to the surface, a laser beam isapplied to the surface at positions where it is desired to have thepalladium remain according to a desired palladium pattern 105. The laserbeam has an energy and/or wavelength chosen to decompose the palladiumprecursor (e.g., palladium carboxylate) to form elemental palladium thatadheres to the surface. After the laser writing process is complete, thesubstrate may be washed or otherwise treated in a manner that removesthe unreacted palladium precursor from the surface. At the end of thisprocess, a pattern of elemental palladium 104 remains on the surface atdesired locations according to the desired palladium pattern. Spatialresolution of the active palladium pattern then depends on the spatialresolution of the laser and/or its actuators.

As mentioned above, the decomposition of a palladium precursor may useany combination of heat, an e-beam, an ion beam, a laser, or the like.An e-beam or an ion beam also permits actuated control of a small beamthat permits patterning of the palladium precursor. Pattern resolutionwill depend on the actuation and size of the beam. Optics may be used todecrease beam size increase resolution of pattern 104.

Returning back to FIG. 6A, the output of printing apparatus 180 is asubstrate with the palladium precursor solution printed thereon. Asmentioned above, this may be with a specific pattern that resembles adesired final pattern for conductive lines a substrate and circuit (FIG.4A), or a blank patterning that requires subsequent scribing to achievethe desired circuit pattern.

Evaporation apparatus 190 receives the substrate and exposes thepalladium precursor solution to conditions that promote evaporation of asolvent from the palladium precursor solution to leave a palladiumprecursor 22 on the substrate. Evaporation apparatus 190 may include anysystem for transferring heat (or another form of energy) to thesubstrate and/or solvent. Heat transfer via conduction, convection,radiation, and combinations thereof, are suitable for use with apparatus190. Evaporation apparatus 190 may vary with printing apparatus 180. Forexample, Gravure printers often use a gas fired or electric fired drierto dry the Gravure ink and drive off any solvents or water, whichessentially replaces most of the solvent, from the substrate. An inkjetprinter may use rollers with an elevated temperature to transfer heat tothe substrate and dry the palladium ink Evaporation apparatus 190outputs a circuit precursor 23 that includes palladium precursor 22 on asubstrate 20.

In one embodiment, the evaporation process is coupled with palladium inkdeposition. For example, the palladium ink 210 may be partiallypre-heated as it is disposed on the substrate. A second round of heatingthen evaporates the solvent from the substrate, albeit with less energythan normal since the ink has already been pre-heated.

In another embodiment, solvent evaporation is coupled with thedecomposition process. In this case, evaporation apparatus 190 is partof a larger apparatus that also performs decomposition of the palladiumprecursor.

In yet another embodiment, a separate chamber 190 is provided solely forevaporation. For example, this may include a curing oven whose thermalperformance is adapted to specifically evaporate solvent from circuitprecursors 23. In many processes in which a pattern of active palladiumis to be formed on the surface at a high resolution, it may be desirableto first evaporate solvent from the deposited palladium ink—and onlyafter this to decompose the palladium precursor to form the palladiummetal ink pattern. To this end, it is desirable to expose the substrateand/or solution to conditions that promote evaporation and transfer heatto the solvent prior to conditions that decompose the palladiumprecursor (e.g., palladium carboxylate). This reduces the likelihood of“smudging” the ink pattern that is to remain on the substrate. This isparticularly useful in sub-ten micron patterning.

Turning now to FIGS. 5 and 6B, printing reservoir 200 will now beexpanded upon. The manufacture and construction of printing reservoir200 will also vary with the type of printing apparatus 180. In general,the function of printing reservoir 200 is to store a palladium precursorsolution 210. For a particular inkjet printer, printing reservoir 200will mechanically and electrically resemble a printer cartridge designedto interface with that particular inkjet printer. For Gravure printing,printing reservoir 200 will resemble the ink reservoir according to aparticular Gravure apparatus.

Printing reservoir 200 may often be sealed prior to usage to extendshelf life of palladium precursor solution 210. Further description ofshelf life and selecting chemical components to extend shelf life aredescribed below with respect to solution chemistry.

FIG. 5 shows a method 150 for manufacturing printing reservoir 200 inaccordance with one embodiment of the present invention.

Method 150 begins by adding a Lewis base ligand (nucleophile) and apalladium compound such as palladium carboxylate to a solvent to createthe palladium precursor solution 210 (152). In a specific embodiment,palladium propionate was prepared by treating commercially availablepalladium acetate in excess propionic acid. The mixture was maintainedat about 40° C. for about 24 hours followed by removal of excesspropionic acid under a vacuum at room temperature. The resulting solidis soluble in amyl acetate. In another specific embodiment suitable forprinting on polyester, a solution of palladium propionate having 0.05%palladium by weight was prepared in amyl acetate Aniline was added in astoichiometric amount that corresponds to 2 moles of aniline per gramatom of palladium. This clear solution was then suitable for printing.Another suitable composition include a 1:1 mole ratio of pyridine and a1:2 complex with cyclo pentyl amine (2 moles of cyclo pentyl amine pergram atom of palladium). The particular Lewis base ligand, palladiumcompound, and solvent will depend on an application, and may also varywith the printing apparatus used. Further description of the chemistryincluded in palladium precursor solution 210 is described below.

Rheological requirements for ink used in each of the printingtechnologies described above may vary. In one embodiment, palladiumprecursor solution 210 is adapted during manufacture to one or morerheological properties of a fluidic dispensing requirement of a printer(154). The rheological property may include one or more of: surfacetension, density and viscosity (and combinations thereof) for palladiumprecursor solution 210 and/or a rheological fluidic dispensingrequirement of a printer. For example, Gravure inks preferably include alow viscosity that allows them to be drawn into engraved cells in acylinder and then transferred onto a substrate. Many inkjet printerstune the waveform supplied to their piezoelectric actuator according torheological properties of their preferred ink, e.g., for quality controlof printed output Inks with rheological properties that do not match thetuned waveform often produce lesser quality printed output. Providing anew or different ink, such as palladium precursor solution 210, to acommercially available in general-purpose inkjet printer may thenrequire the ink to conform to a tuned waveform or other printingapparatus rheological property.

The present invention contemplates multiple ways to adapt palladiumprecursor solution 210 to a rheological property of a fluidic dispensingrequirement of a printer. In one embodiment, the palladium precursorsolution is adapted to the rheological property of the fluidicdispensing requirement. In this case, one or more of the Lewis baseligand, palladium compound, and/or solvent selected to provide aparticular aggregate rheological property for palladium ink 210. Forexample, the solvent may be chosen with particular density or viscosityto match that desired by a particular printing apparatus 180.

In another embodiment, the palladium ink includes an additive thatadjusts a rheological property of the palladium precursor solution to arheological property of a fluidic dispensing requirement of printingapparatus 180. For example, the additive may include a surfactant thatchanges surface tension and/or density of palladium ink 210. Surfacetension of palladium ink 210 often affects droplet size for an inkjetprinter that deposits the ink onto a substrate. The particular substratematerial may also affect surface tension for the printer; paper oftenhas a different droplet size then a smooth surface associated with apolymer such as polyimid. In either instance, the surfactant may beselected to achieve a desired droplet size for a particular inkjetprinter and a particular substrate material. Preferably, the additive isselected to be chemically inert to the active palladium left on thesubstrate. In one embodiment, the additive is selected to also bechemically inert to the printing apparatus.

Other additives may be included in palladium ink 210. It is generallydesirable for palladium ink 210 to not substantially corrode one or morecomponents of printing apparatus 180. Since the palladium precursorsolution 210 may be used with off-the-shelf general-purpose printers andmay include chemistries not intended for these general-purpose printers,corrosion of printing components may occur. In this sense, corrosionrefers to dissolving of palladium ink 210 into one or more components ofthe printer, chemical attachment of palladium ink 210 into one or moreprinter components, softening of the printer components due to thepresence of palladium ink 210, or any change in a mechanical or physicalproperty of a printer component. As the term is used herein, substantialcorrosion refers to functional degredation of one or more chemical ormechanical properties for components in a printing apparatus 180. Forexample, an ink solution should not corrode plastic components in aprinter to the point where the components soften, are penetrated by theink, or lose mechanical tolerances. In one embodiment, one or more ofthe Lewis base ligand, palladium compound, and/or solvent are selectedto avoid printer component corrosion. Ideally, there is zero degradationover time. In one embodiment, a time limit quantifies the substantialcorrosion. In one embodiment, substantial corrosion refers to noticeablefunctional or performance degredation of a printing apparatus or acomponent after about 6 months of ink use. In a specific embodiment,substantial corrosion refers to noticeable functional degredation of theapparatus after about 3 months. In another specific embodiment, thepalladium precursor solution has a shelf life, where the palladiumprecursor solution is at least 90 or 95 percent intact, of greater than1 month when added to the solvent.

The present invention then stores the palladium precursor solution 210in a printing reservoir 200. The reservoir may resemble a cartridge thatmechanically interfaces with a general-purpose printer such as anoff-the-shelf inkjet printer. Alternatively, reservoir 200 mayphysically resemble an ink well used in Gravure printing.

The palladium precursor solution 210 may be characterized by theconcentration of palladium included therein. In one embodiment, solution210 includes a concentration between about 0.5 percent and about 0.002percent palladium by weight. In a specific embodiment, solution 210includes a concentration between about 0.05 percent and about 0.2percent palladium by weight.

Having described circuit manufacturing and printing processes, chemistrysuitable for use with the present invention will now be expanded upon.

Previous attempts to form structures reliant on palladium seed layers bydecomposing a deposited palladium compound have been ineffective. Whilenot wishing to be bound by theory, it is believed that these attemptsfailed to form isolated palladium atoms on the substrate and thereforedid not provide good adhesion. The prior palladium deposition techniquestypically employed palladium precursors that would tend to form groupsor agglomerates of associated palladium atoms on the substrate surface.These groups of palladium atoms do not adhere well to most substratesurfaces.

The inventors have identified and developed the concept of “active”palladium. This is palladium metal that has two desirable properties:(1) it is catalytic for subsequent addition of a metal onto thepalladium (such electroless deposition), and (2) it anchors thedeposited metal to the underlying substrate. In some cases, the activepalladium may also be characterized as being disposed monatomically oreven sub-monatomically on the substrate. At some point in the process,the deposited palladium should have approximately zero valence.

The estimation of active palladium as generally having a zero valencerecognizes that the deposition process may not be perfect in forming allpalladium with a zero valence, and minor amounts may stray therefrom.Elemental palladium with a zero valence is particularly active, andwell-suited to initiate attachment with copper or another metal used inthe conductive lines. As mentioned above, elemental palladium does notreadily bind to a surface monatomically, and needs to be deliberatelyprocessed to achieve such a state.

Deposition chemistry and processing techniques chosen by the inventorsprovide strong active palladium anchoring by leaving isolated monatomicpalladium (rather than clusters of palladium atoms), and by producingapproximately zero valence atoms on the substrate. For example,palladium carboxylate precursors, decomposed with suitable input energy,leave isolated palladium atoms with approximately zero valence on thesubstrate after decomposition. The active palladium atoms so depositedcan bind to both the substrate and a metal subsequently depositedthereon. The palladium atoms then act as individual and separateanchoring points between the substrate and metal, which promotes betteradhesion of conductive lines. In some ways, the deposited palladiumatoms resemble atoms deposited on a substrate by a physical vapordeposition technique such as sputtering.

The palladium chemistry and deposition techniques invented by theinventors emphasize process conditions and starting products that arebelieved to promote formation of isolated palladium atoms on a substratesurface. This is believed to be in contrast to prior techniques. Incertain embodiments, it is believed that, in addition careful selectionof palladium solution components, the deposition technique can have apositive impact on the quality of active palladium deposited. In oneexample, the process involves first driving off solvent from a depositedpalladium solution, and then decomposing the remaining material usingadded energy (e.g., using an ultraviolet source or laser for example) toproduce the active palladium.

It has been recognized by the inventors that palladium compounds such aspalladium carboxylates easily form loose assemblies such as dimers andtrimers in solution. In these assemblies, the palladium atoms ofindividual molecules may cluster head to head. The inventors discoveredthat without addressing this phenomenon, the resulting elementalpalladium formed after decomposition does not adhere well to thesubstrate. Adding a strong Lewis base (e.g., a stronger electron donorthan the carboxylate or other anion in the palladium precursor) maybreak the bridging between palladium compounds and form a solution inwhich the palladium precursor compounds remain relatively isolated fromone another. When the palladium precursor from such solution isdecomposed on a substrate surface, it is believed that elementalpalladium tends to deposit as individual atoms rather than as a cluster.This forms essentially monatomic anchor points for the palladium itselfas well as subsequently deposited copper or other metal.

Generally, the palladium precursor solution includes a Lewis base ligandand a palladium compound in a solvent. The choice of a particularpalladium precursor and solvent may be dependent upon a particularsubstrate on which the palladium and subsequent conductive lines will bedeposited, or a particular manufacturing process, as one of skill in theart will appreciate.

Before providing an expanded description of particular components, oneor more optional desirable properties of a palladium precursor solutionwill first be discussed. Constituents of the palladium precursorsolution may be selected to produce one or more properties. In oneembodiment, the solvent, palladium-containing compound and Lewis baseligand are all organic substances. Suitable examples are describedbelow. In another embodiment, the Lewis base ligand and a palladiumcompound are selected such that decomposition products of the palladiumprecursor solution decompose relatively easily. For example, theconstituents may be selected to have a certain decompositiontemperature. The Lewis base ligand and a palladium compound may also beselected such that decomposition products are benign and/or easilyremoved. Examples of suitable decomposition products include carbonmonoxide, carbon dioxide, water and a fragmented or an unfragmentedligand. When the decomposition uses heat or high energy, the water oftenreleases as a vapor.

In addition, the decomposition products preferably do not affect thesubstrate being printed upon. In one embodiment, none of thedecomposition products are oxidizers or strong reducing agents. Again,decomposition by-products such as carbon monoxide, carbon dioxide, andwater are suitable in this regard.

In another embodiment, the palladium-containing compound is chosen suchthat the palladium precursor solution has a sufficient shelf life for adesired application. As the term is used herein, shelf life refers tothe rate of functional decomposition of the palladium precursorsolution. Preferably, the solution does not decompose at any measurablerate, or has no technical decomposition by a certain date defined by theshelf life. Decomposition may appear as metallic deposits or visualprecipitation in the solution in which the palladium decomposes out ofthe solution onto walls and other structures. In one embodiment, theshelf life is greater than three or six months, and more preferablygreater than 6 weeks. Of course if the intent is to use the precursorsolution immediately or very soon after it is created, shorter shelflives may be acceptable. In a specific embodiment, the palladiumprecursor solution has a shelf life, where at least 95% by weight of thepalladium precursor remains intact, for longer than 3 months after thesolution is formed. Even longer shelf lives may be desirable in somecontexts, particularly those in which extended storage may be needed. Asdescribed above, the present invention is well-suited for use withprinting technologies where the palladium precursor solution is storedin a reservoir or ink cartridge used with a printer. Storage in such areservoir may occur for months or years before use, and the inkcartridge may remain in a printer for months or years once installed.Selection of a palladium-containing compound to promote solutionlongevity is thus important in ink distribution business models andapplications such as these. Selection of an inert material for the inkreservoir, such as glass or an inert polymer or polymer coating, alsoextends shelf-life.

In another embodiment, constituents of a palladium precursor solutionare chosen to facilitate deposition of the solution. Four such examplesare now provided.

Example #1 Preparation of Palladium(II) Propionate

5 gm commercial palladium(II) acetate trimer (Aldrich) was added to 40 gof propionic acid. The mixture was maintained at 40 degrees Celsius for24 hours. Excess propionic acid was removed under vacuum at roomtemperature. The resulting yellow solid was used for making palladiuminks.

Example #2

0.075% palladium (II) solution in amyl acetate was prepared bydissolving 0.357 g of palladium (II) propionate, prepared as describedin Example #1, in 199.643 g of amyl acetate. The solution thus formedwas filtered through 0.45 μm PTFE acrodics. 0.241 g of cyclopentylamine(2 equiv. w.r.t. Pd atom) was added to the clear solution. The solutionimmediately turned from brownish yellow to pale yellow. Two polyestercoupons of “5.5×6” inch and “5×9” inch were dipped in this palladium(II) solution for three minutes and heated on a hot plate kept at 160degrees Celsius. The coupons were dipped in electroless copper solutionfor about 1 minute. A uniform copper layer developed on substrate.

Example #3

0.125% palladium (II) solution in amyl acetate was prepared bydissolving 0.297 g of palladium (II) propionate (prepared as describedin Example #1 above) in 99.703 g of amyl acetate. 0.337 g oftripropylamine was added to the clear solution. Polyester coupons of“9×9” inch were coated with this solution using camel brush at 50degrees Celsius and kept in oven at 130 degrees Celsius for 8 minutes.The coupons were dipped in electroless copper solution. A uniform layerof copper developed on substrate.

Example #4

0.125% palladium (II) solution in amyl acetate was prepared bydissolving 0.297 g of palladium (II) propionate (prepared as describedin Example #1 above) in 99.703 g of amyl acetate. 0.239 g ofDiisopropylamine was added to the clear solution. A polyimidesubstrate“5×6” was dip-coated in this solution, air dried and heated at170 degrees Celsius for 5 min. The coupon was dipped in electrolesscopper solution until a uniform copper layer is deposited on thesubstrate.

Palladium precursor solution components may also be tuned to anapplication. As described above, solution components may be selected toadapt one or more rheological properties of the fluid that are importantfor printing. Alternatively, solution components may be selectedaccording to a specific substrate being printed on; specific examplesare provided below.

The palladium precursor solution components will now be separatelyexpanded upon.

The palladium-containing compound in the palladium precursor solutionacts as a palladium carrier. The palladium-containing compound may beselected according to one or more of the following properties: a) besoluble in a particular solvent employed in the palladium precursorsolution; b) be compatible with the chosen Lewis base ligand (e.g., be aweak Lewis acid); and/or c) be relatively inexpensive.

Various palladium carboxylates meet most or all of these criteria. Inone embodiment, it is desirable to limit the size of a carboxylate toten carbons or less. In another embodiment, it is desirable to limit thesize of a carboxylate to six carbons or less. In a specific embodiment,the palladium carboxylate has two to five carbon atoms. In anotherspecific embodiment, the palladium carboxylate has three to five carbonatoms. One preferred carboxylate is a propionate. Examples of otherpalladium carboxylates that may be employed are in some embodiments arepalladium acetate, palladium oxalate, and palladium iso-butyrate. Notethat use of relatively short chain carboxylates may help avoid theundesirable decomposition processes that produce elemental carbon. Ingeneral, while palladium is bivalent it need not have two separatecarboxylate groups. In some examples, the carboxylate may include 2 ormore carboxylic acid groups (e.g, it could be an acetate and aproprionate). Further, the carboxylate can be fully saturated or includeone or more unsaturated bonds, and it can be straight chained orbranched. For dicarboxylic acid compounds, one of the carboxylate groupscould be separately reacted to form an ester.

The palladium-containing compound may be selected to have a good shelflife when not in a solution, in addition to its shelf life when insolution. For example, the palladium compound may not includehygroscopic properties so as to avoid degradation over time byattracting water. Palladium (ii) acetate is suitable in this regard.

As mentioned, decomposition properties of the palladium compound mayalso affect selection (along with decomposition properties of the Lewisbase ligand, as described below). For example, palladium carboxylateshaving a decomposition temperature in the range of about 100° C. to 240°C. are desirable in some embodiments. The choice of corresponding ligandwill sometimes impact the decomposition temperature. Lewis base ligandsthat may be used with palladium carboxylates and allow decomposition inthe above temperature range include cyclopentylamine, triethyl amine,diisopropyl amine, etc. Palladium proprionate has a decompositiontemperature of about 130° C. (oven temperature) when used withtriethylamine as a Lewis base ligand.

As mentioned, a Lewis base ligand may be provided in the palladiumprecursor solution to facilitate formation of active palladium. Asalluded to above, it is believed that the presence of a Lewis baseinterferes with the natural tendency of palladium carboxylate moleculesto bridge with one another in solution. Therefore, in certainembodiments, a strong Lewis base is provided to the palladium precursorsolution to coordinate with available spaces on a palladium that are notoccupied by carboxylate groups. In the embodiments described here, theLewis base acts as a ligand for the palladium compounds. In a simplisticview of the chemistry, palladium has four separate coordination sitesthat may be occupied. In palladium carboxylates, carboxylic acidmoieties occupy two of these sites (because palladium has a valence oftwo). The remaining two sites may be occupied by other palladiummolecules, by complexing groups, etc. In the embodiments described here,the Lewis base ligand may occupy one or two available sites on thepalladium and sterically hinder access to those sites by other palladiumcarboxylate molecules, etc. Thus, introducing these ligands may minimizebridging between individual palladium carboxylate molecules andfacilitate deposition of the palladium atoms on the substrate in anisolated fashion. Again, this is believed to provide better adhesion ofthe elemental palladium to the underlying substrate and better shelflife to the palladium ink.

The Lewis base ligands may be any material that meets the variousconstraints for an application (e.g., for use with a specific ink jetprinter) and interferes with solution phase bridging between palladiumcompounds without decomposing them. Examples include various nitrogencompounds, phosphorous compounds, sulfur compounds, etc.Nitrogen-containing compounds are particularly well-suited to stabilizemany palladium precursors such as palladium carboxylates. Examples ofnitrogen-containing compounds include nitrogen donors such as primary,secondary and tertiary amines with a general formula RNH₂, R₁R₂NH, orR₁R₂R₃N, whose R=C_(n)H2_(n+1) and n=1 to 15, (R₁R₂R₃ may be similar ordissimilar), etc. The amines may be aliphatic or aromatic, straightchain or branched, and with or without unsaturation. Specific examplesinclude, for example, cyclopentylamine, tri-ethylamine, pyridinecarboxylates, pyridine, aniline, tetramethylethylenediamine,dimethylamine, and di-isopropylamine. In certain embodiments, themolecular weight of the Lewis base is between about 30 and 200, morepreferably between about 45 and 145. However, in some situations, it maybe appropriate to employ larger molecules or even polymers such aspolyimines. This may be appropriate when, for example, it is desired toincrease the viscosity of the palladium precursor solution.

To produce elemental palladium on the substrate, the Lewis base ligandswill, in most embodiments, need to be removed. This can be accomplishedby either volatilization (depending on the vapor pressure of the base)or decomposition (along with the palladium precursor). Decomposition ofa nitrogen-containing base may produce a fragmented or an unfragmentedamine.

In some embodiments, the Lewis base is a polar species and may thusrequire the use of a polar solvent. In certain embodiments, aqueoussolvents may be appropriate; i.e., water may serve as a solvent, in partor in whole.

Other factors may enter choosing a Lewis base. Selection of the Lewisbase ligand will also affect shelf life of the palladium precursorsolution and thermal stability in palladium precursor after the solventis evaporated away. For example, cyclopentylamine or diisopropyl aminewill generally improve shelf life. Thermal stability affects shelflife—and the ease of removing the palladium precursor from thesubstrate. Thus, the Lewis base ligand should readily volatilize whendecomposed and separated from the palladium, but not be subject todegradation within handling temperatures. Smaller molecular-weightligands, such as pyridine, diisopropyl amine, and cyclopentyl amine areparticularly well-suited in this regard. In another embodiment, theLewis base ligand is selected to give a decomposition temperature forthe palladium precursor that is less than the melting temperature of thesubstrate. Choice of the Lewis base ligand will then depend, in part, onthe substrate being used. Diisopropyl amine and triethyl amine in amolar ratio of 1:1 is suitable for use with polyester for example.

The Lewis base ligand will also affect rheological properties of thesolution. Thus, in certain embodiments, the rheological properties ofLewis base are considered in making a decision on which compound to use.For example, tri-ethanol-amine acts as both a suitable Lewis base and asa surfactant.

The solvent may be selected according to a number of factors. In oneembodiment, the solvent is a polar molecule or a combination of polarmolecules. In some embodiments, the solvent is aprotic, preferablycomprised of one or more polar aprotic compounds. Thus, the solvent maybe a) polar or non-polar, b) aprotic or protonic, or any combination ofa) and b). The solvent should be chosen so that it does not interferewith the balance between the Lewis base ligand and the palladiumprecursor compound.

Some suitable solvents include glycol ethers, methanol, amylacetate,gamma-butyrolactone, water, ethylene glycol, di-ethylene glycol,propylene glycol, isobutyl acetate, DMF, tetramethyl urea, toluenehexane, cyclohexanone, terpeneol, 2,2-dimethoxy propane, chloroform,dichloromethane, ethylene carbonate, ethylene glycol, diethylene glycoldimethyl ether, propylene glycol monomethyl ether acetate, butylacetate, hydrocarbons such as toluene, xylenes, cyclo hexanone, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, iso amyl acetate.A mixture of two or more of these solvents may also be used.

Choice of the solvent may be influenced by the intended process forremoving it from the deposition substrate. If evaporation is chosen, thesolvent should have a relatively high vapor pressure at the temperatureemployed to remove the solvent. In addition, heat capacity can affectthe choice of a solvent. Note that the evaporation rate stronglyinfluences the speed and spatial accuracy of pattern manufacture asdescribed above. Mixtures of solvents may then be varied to achieve adesired evaporation temperature.

As mentioned above, rheological properties of the solvent may alsoaffect solvent selection. Appropriate rheological properties for solventselection include density, viscosity, and surface tension. The solventrheological properties may also be selected relative to a particularsubstrate being used; liquid and droplet performance on paper is oftendifferent than on a plastic material. A mixture of amyl acetate andglycol ethers is well-suited as a solvent for use with polyimid. Choiceof solvent rheological properties may also be affected by a printingapparatus or dispensing mechanism in the printing apparatus, e.g., toreduce viscosity for Gravure printing as described above. In addition,since printing resolution is often affected by solvent properties,surface tension for the solvent may be modified in order to increaseresolution of a printed pattern.

The palladium ink also may include a solvent that is chosen for acertain combination of the properties listed above (e.g., it may dictatethe viscosity, evaporation rate, and surface tension of solution).

The solvent must also be compatible with any components in the printingapparatus used to deliver the palladium ink. For example, seals on manycommercially available printers may include an elastomer that corrodesin the presence of certain chemicals. Plasticizers for example, whichmay be included in the palladium precursor solution 210, are commonlyknown to corrode plastic materials. Other components in a printingapparatus that may corrode include plastics, ceramics and metalcomponents such as those used in a gasket, O-ring or seal. If theprinter is known to have these or other chemical sensitivities, then thesolvent may be selected to avoid corrosion of such parts. Suitablenon-corrosive solvents include diethylene glycol diethyl ether.

Having described manufacturing processes suitable for use with thepresent invention, along with suitable chemistry, alternative forms ofmanufacture suitable for use will now be discussed.

The present invention also enables roll-to-roll and other forms ofcontinuous throughput manufacturing. Continuous throughput manufacturingpermits circuit precursors and circuits to be efficiently produced inhigh-volume, and reduces the cost of individual circuits mass-producedin this manner.

FIG. 8 illustrates a continuous throughput manufacturing process 300 inaccordance with one embodiment the present invention. FIG. 8 also showsthe manufactured product at each manufacturing stage.

Manufacturing process 300 begins with providing a substrate 303 off aroll of substrate material 302. For example, roll 302 may include a rollof thin polyester or polyimid tape.

Each layer from the roll 302 is provided to a printing apparatus 180,which deposits a palladium precursor solution onto the substrate. As oneof skill in the manufacturing arts will appreciate, there are numeroustechniques suitable for automated supply of a substrate between roll 302and printing apparatus 180.

Substrate with palladium precursor solution printed thereon (305) isprovided to curing oven 304, which evaporates the solvent from thepalladium precursor solution. Curing oven 304 also decomposes thepalladium precursor to produce elemental and active palladium on thesurface of the substrate. Output of curing oven 304 are circuitprecursors 307 that include active and elemental palladium on a surfaceof the substrate in a pattern that resembles a desired pattern forconductive lines to be subsequently added. As mentioned before, thepalladium pattern may be established during palladium precursor solutiondeposition in printing apparatus 180 or during selective decompositionin curing oven 304.

The circuit precursors 307 are then provided, by automated means, toelectroless copper deposition station 306. Electroless plating, alsoknown as chemical or auto-catalytic plating, is a non-galvaonic type ofplating method that involves several simultaneous reactions in anaqueous solution, which may occur without the use of external electricalpower. The reaction is accomplished when hydrogen is released by areducing agent, such as sodium borohydride, and oxidized thus producinga negative charge on the surface of the part. The most commonelectroless plating methods are electroless nickel and copper platings,where the chemistry for each may vary significantly. In one embodiment,electroless copper deposition includes submersing a circuit precursor ina solution that includes copper ions, a reducing agent, a buffer tomaintain a certain pH and a complexing agent. In general, manufacturingprocess 300 may use any commercially available electroless depositiontechnique or apparatus. Metals added via electroless plating includegold, silver, copper, nickel, rhodium, and palladium, for example. Theexact chemistry and steps will vary with the type metal.

One suitable electroless copper process consists of four stages:cleaning, activation, acceleration, and deposition. The cleaning stageuses a cleaner-conditioner to remove organics and condition patternfeatures for the subsequent uptake of a catalyst. Thecleaner-conditioners often include an alkaline solution. An optionalmicro etch step may follow the cleaning; the micro etch processing stepcan be used in an electroless line, oxide line, pattern plate line, orwith chemical cleaning. Activation, through use of a catalyst, reducesthe positive ion metal being added. Common activation catalysts includetin chloride, or palladium chloride. Acceleration removes the remainingpositive metal ions from the pattern. Fluoboric acid is a commonaccelerator, as is sulfuric acid with hydrazine.

Electroless copper deposition and baths can be divided into two types:heavy deposition baths (designed to produce 75 to 125 micro-inches ofcopper) and light deposition baths (20 to 40 micro-inches). Electrolyticcopper plating commonly follows light deposition. Heavy deposition cansurvive the outer layer imaging process, with copper electroplatingoccurring thereafter. Common constituents of electroless copperchemistry are sodium hydroxide, formaldehyde, EDTA (or other chelater)and a copper salt. In one specific complex reaction, catalyzed bypalladium, formaldehyde reduces the copper ion to metallic copper.Formaldehyde (which is oxidized), sodium hydroxide (which is brokendown), and copper (which is deposited) must be replenished frequently.Many heavy deposition baths have automatic replenishment schemes basedon in-tank colorimeters. Light deposition formulations may be controlledby analysis. An anti-tarnish bath may be used after deposition.

Output of copper deposition station 306 is a circuit 309 with copperdisposed over the active and elemental palladium according to thepalladium pattern.

The circuits 309 then provided, again by automated means, toelectroplating station 308. Electroplating deposits additional metalused in the conductive lines. Electroplating is the process by which ametal in its ionic form is supplied with electrons to form a non-ioniccoating on a desired substrate. One common electroplating systeminvolves a chemical solution which contains the ionic form of the metal,an anode (positively charged) which may consist of the metal beingplated (a soluble anode) or an insoluble anode (usually carbon,platinum, titanium, lead, or steel), and finally, a cathode (negativelycharged) where electrons are supplied to produce a film of non-ionicmetal. Electroplating may not be necessary when enough copper or metalhas been deposited by electroless deposition station 306, but iscommonly used after a light deposition. Electroplating may include afull panel plating, which adds about 1 mil on the surface, or a “flash”panel plating, designed only to add small amounts of copper.Flash-plated panels return to copper electroplating to be plated up to arequired thickness.

Output of electroplating station 308 is circuits 311 printed on thesubstrate 302. In this case, the circuits are provided back to a roll310 for easy shipping of the individual circuits 311 in a common roll.

Roll-to-roll manufacturing as demonstrated by manufacturing process 300permits automated manufacture by pulling a common line of polyimid (oranother rolled and flexible material) substrate over a number of rollers314 along the manufacturing process. This reduces substrate handling,increases manufacturing speed and efficiency, facilitates high volumemanufacturing, and permits for centralized automated control of eachstage in manufacturing process 300.

The present invention is thus well-suited for high throughputmanufacture of small circuits. FIGS. 9A and 9B illustrate automatedmanufacture of RFID devices in accordance with a specific embodiment ofthe present invention.

FIG. 9A illustrates an exemplary RFID device 350 in accordance with aspecific embodiment of the present invention. RFID device (or RFID tag)350 includes a chip 352 and an antenna 354. Chip 352 may be anycommercially available RFID chip, such as those commercially availablefrom a wide variety of vendors such as Motorola. Antenna 354 permitscommunication between chip 352 and an external RFID reader, and includesa pattern 356 of conductive lines on the surface of a substrate 358.

FIG. 9B illustrates the automated manufacturing process 360 of RFIDdevice 350 according to techniques of the present invention.Manufacturing process 360 begins by rolling a polyester substrate from aspool 362.

The polyester substrate is then continuously fed through a Gravure orother rolled printing apparatus 364 that deposits palladium ink onto oneor more surfaces of the polyester substrate. The Gravure printingapparatus 364 operates at high speeds to produce a palladium patternthat resembles the final antenna pattern 356. Since the final RFIDdevice 350 may be quite small and often in the range of a fewmillimeters or less in size, while the roll for Gravure printingapparatus 364 may be substantially larger and up to a meter in diameter,hundreds or thousands of a palladium antenna patterns (depending on thewidth of the polyester material supplied to the roll) may be producedfor each turn of the roll in printing apparatus 364.

The printed palladium solution patterns on the polyester substrate arethen provided to decomposition apparatus 366, which generates activepalladium on the surface of the polyester substrate by supplying energyto a) first evaporate the solvent from the solution, and then b) toconvert the palladium precursor to active palladium. In this case,decomposition apparatus 366 supplies one of: hot air, ultravioletenergy, or infrared energy to supply energy for both a) and b). Forexample, an infrared lamp disposed proximate to the substrate as itpasses by may be suitable to provide enough energy for both phases ofprocessing.

Copper is then added to the palladium precursor patterns on thesubstrate (according to the location of the patterns on the substrate)to form the metal antenna 354. As shown, manufacturing process 360 usesboth electroless copper deposition 368 and copper electroplating 370,which were described above with respect to FIG. 8.

The automated process then transports the substrate and antenna to anoptional die-attach station 372, which adds chip 352 to each RFID device350. This may use any robotic or automated technology suitable forplacing small devices on the polyester substrate.

FIG. 9C shows the printed output 375 of manufacturing process 360, whichincludes numerous RFID devices on the roll material before being cut, inaccordance with a specific embodiment of the present invention. Asshown, the RFID devices 350 remain on a common polyester substrate andare rolled back onto an RFID device spool 374. In another embodiment,the substrate is cut to produce separated RFID devices that areindividually packaged as output of manufacturing process 360.

The present invention finds wide use. Provided now are severaladditional exemplary products and applications; the following examplesare not meant to be exhaustive, and the present invention finds use inother applications not mentioned herein for sake of brevity.

RFID devices as produced above are suitable for use in the followingapplications: package and parcel tracking, baggage handling systems usedin airports, animal tracking on farms, inventory management, libraries,document management, electronic toll systems, car identity, ski tickets,medical goods, anti-counterfeiting of monetary currencies, electronicsecurity surveillance of articles such as clothing goods, access controlsuch as requiring security personnel to carry on RFID device, etc.

Circuits produced according to the present invention find wideapplication. Specific circuits include placing a palladium layer onelectrical contacts, multi-chip modules, printed wiring boards, andPCMCIA (Personal Computer Memory Card International Association) cards.This includes computer chips, packaging for chips, and layered circuitdesigns are also suitable for production with methods described herein.The present invention also presents an alternative to electroplating andvacuum and adhesive deposition techniques currently used for addingconductive lines, and is applicable in most applications that theseconventional fabrication techniques are employed.

As mentioned previously, the present invention is well suited to produceflexible circuits disposed on a flexible substrate. Since the activepalladium patterns do not require rigid support of the underlyingsubstrate, circuit precursors produced according to FIG. 1 may beshipped and handled without compromising subsequent copper deposition.The flexible circuits may also remain flexible after copper depositionand conductive line formation.

Flexible conductive circuits made at high throughputs and low costenables circuit usage in a variety of new and existing applications.FIG. 10A shows a tracking label 400 that includes a layered design inaccordance with a specific embodiment of the present invention. Thelayered design includes an outer layer 402, an intermediate layer 404,and a release layer 406. Outer layer 402 provides visual output fortracking label 400 and may be made from paper or a pressure-sensitivefacestock. Intermediate layer 404 includes an RFID antenna and chip thatpermits wireless communication and tracking of label 400. Intermediatelayer 404 may be mass produced according to techniques described herein.Release layer 406 includes a release coated liner, such as those thatinclude a peal-off adhesive. Tracking label 400 is thus well-suited forthe shipping industry where large number of packages are sent andtracked on a daily basis. Release layer 406 permits easy of use, whilethe RFID antenna in intermediate layer 404 permits wireless tracking,which simplifies usage relative to conventional optical trackingtechnologies that require a shipping employee to manipulate and opticalreader within line of sight of the tracking label. Alternatively, thepresent invention permits an RFID reader to be stored on a truck ordelivery vehicle, where the RFID reader automatically and wirelesslylogs every package loaded onto the truck and every package subsequentlydelivered from the truck.

The present invention also enables circuit printing on conformalsurfaces. Exemplary conformal surfaces includes those found in cellphones, GPS systems, consumer electronics devices, etc.

FIG. 10B shows an inner surface of a housing 420 used in a cell phonethat includes a conformal surface and circuit 422 printed thereon inaccordance with a specific embodiment of the present invention.Disposing circuit 422 on housing permits the cell phone to include oneless structure dedicated specifically to a circuit. This reduces volumeof the cell phone, and may lead to even thinner cell phone profiles.

The present invention also permits metal deposition onto non-circuitstructures. For example, circuit components, such as antennae, may bemade using techniques described herein. The substrate may include afiber. These (and other non-metal coated fibers) may be used to create awoven structure or fibrous material. In one embodiment, patterns are notdisposed on individual fibers, however, patterns may be created byweaving in a process that optionally employs both coated and uncoatedfibers. As mentioned above, oddly shaped substrates may be field coated,such as brushes and their individual bristles, sponges, hook and loopfasteners, etc.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Therefore, the present examples are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope of theappended claims.

1. A circuit, comprising: a substrate having a first surface; a precursor pattern that is monatomically disposed on the first surface of the substrate, wherein the precursor pattern does not by itself form a layer that electrically conducts along the substrate; and a set of conductive lines that are disposed on the first surface of the substrate according to the precursor pattern.
 2. The circuit of claim 1, wherein the set of conductive lines includes a line with a surface width of less than about 250 microns.
 3. The circuit of claim 1, wherein the set of conductive lines includes a line density of greater than about 1 line per millimeter.
 4. The circuit of claim 1, wherein the substrate is flexible.
 5. The circuit of claim 1, wherein the substrate is non-flat.
 6. The circuit of claim 5, wherein the substrate is included in a housing of a portable electronics device.
 7. The circuit of claim 6, wherein the portable electronics device is a mobile telephone.
 8. The circuit of claim 1, wherein the set of conductive lines is formed from copper.
 9. The circuit of claim 1, wherein the precursor pattern is formed from active palladium.
 10. The circuit of claim 1, wherein the precursor pattern is formed from active palladium.
 11. The circuit of claim 1, wherein the precursor pattern has a surface concentration of less than about 6×10⁻¹⁰ gram atoms per square millimeter.
 12. The circuit of claim 1, wherein the substrate is formed from a polyester material.
 13. The circuit of claim 1, wherein the substrate is a polyimide.
 14. A structure comprising: an electrically non-conductive substrate having a first surface; a conductive layer disposed on the first surface of the substrate; and a precursor that is monatomically disposed between the first surface of the substrate and the conductive layer, wherein the precursor adheres the conductive layer to the electrically non-conductive substrate.
 15. The structure of claim 14, wherein the conductive layer is formed from copper.
 16. The structure of claim 14, wherein the precursor is formed from active palladium.
 17. The structure of claim 14, the precursor has a surface concentration of less than about 6×10⁻¹⁰ gram atoms per square millimeter.
 18. The structure of claim 14, wherein the substrate is a polyimide.
 19. A circuit precursor comprising: an electrically non-conductive substrate having a first surface; and an electrically non-conductive precursor pattern that is monatomically disposed on the first surface of the substrate, wherein the substrate and precursor are adapted to accept thereon a set of electrically conductive lines according to the precursor pattern to form a circuit on the substrate.
 20. The circuit precursor of claim 19, wherein the precursor is formed from active palladium. 